For many years various types of decalcomanias (decals) have been utilized for the decoration of articles or wares of various types, including glassware, china ware, pottery, aluminum, porcelain enamel, etc. These decalcomanias originally included the water or "slide-off" type in which a paper backing had a design layer disposed thereon and the paper carried a thin layer of a water soluble gum with a vitreous design imprinted thereon. Subsequently, however, as this art developed, decalcomanias of the "heat-release" type were developed, including a backing sheet, a design or pigment layer generally formed from inorganic pigments or oxides, and an optional protective layer applied on the design layer. These types of decalcomanias preferably included a release layer disposed between the backing sheet and the design layer to facilitate release of the design from the backing sheet during heating. Examples of typical heat-releasable decalcomanias are disclosed in a number of U.S. patents, including U.S. Pat. Nos. 2,970,076 to Porth; 3,007,829 to Akkeron; 2,991,221 to Bower; 3,411,458 to Milliken; 3,445,309 to Milliken; and 3,642,551 to Laconich et al.
In order to utilize such heat release types of decalcomanias, the article or ware to be decorated is generally preheated and the decalcomania can then be applied to the article with the backing sheet up so that the layer of heat-activatable adhesive directly contacts that article. Thus the heat applied to the article effects both a preliminary bonding of the design layer, via the heat-activatable adhesive, to the article or ware, while the heat also effects the release of the backing sheet, preferably including a barrier layer, and a portion of the release layer, from the design layer. The article can then be fired at high temperatures in the usual manner so that the design layer is melted and permanently fused to the article, and the combustible organic ingredients including the remaining portion of the release layer, the resinous carrier for the design layer, and the heat-activatable adhesive layer are preferably consumed during such firing.
The heat-release layers generally employed in such decalcomanias include those disclosed in the above-noted Porth and Akkeron patents. In particular, these include normally solid mixtures of polyethylene glycol compounds, and preferably as disclosed in the Akkeron patent including at least one polyethylene glycol compound which has an average molecular weight of from about 15,000 to about 20,000. These compounds have generally been employed as alternatives to vegetable or mineral waxes having melting points within the range of from about 130.degree. F. to about 220.degree. F. These types of decalcomanias, as noted above, have been employed for decorating various wares or articles. In connection with same, such decalcomanias of both the "underglaze" and "overglaze" type have been utilized. In the former case, the decalcomania is applied to the ware after its formation, but prior to its being glazed, which is accomplished after application of the decal to the ware. The glazes employed generally comprise vitreous coatings which generally require very high temperatures to form the glass from their raw materials. This procedure thus results in a protective coating over the pigments in the decal, but the high temperatures required tend to destroy certain colors, leaving only a limited color patette. Thus "overglaze" decalcomanias have also been developed in which application to the ware is carried out after it has been glazed. These decalcomanias generally include silk screen and lithographic decals. The present invention is intended for application in connection with all of these various types of decal applications of the heat release type.
In addition, in a recent application of Hazel Meade bearing Ser. No. 742,417, filed on Nov. 11, 1976, now U.S. Pat. No. 4,068,033 a novel heat activatable adhesive composition for use in such decalcomanias is disclosed. This adhesive composition is intended for use in connection with such ware decoration in a manner such that heating of the ware itself can be eliminated. These compositions thus include a "delayed tack" feature whereby the adhesive composition after it has been heated to above its softening point retains its tackiness or adhesive character for a suffacient amount of time for it to be applied to the ware, without the ware itself having to be heated. That portion of the above-noted application to Hazel Meade is incorporated herein by reference hereto, and will be discussed in more detail below in connection with the novel heat release layer of this invention.
The search has therefore continued for a new heat release composition which can be easily applied to the backing sheet, which has a melt viscosity such that release of the design layer is easily facilitated, which does not result in the application of a tacky surface to the outer surface of the design layer after it has been applied to the ware, and which can be completely burned off during firing without any adverse effects to the decoration itself. In addition, the search has also continued for a combination of heat release and heat activatable adhesive layers in such decalcomanias which includes all of these properties with regard to the heat release layer as well as the above-noted properties regarding the heat activatable adhesive layer, including the ability to remain tacky or adhesive after heating for a suitable period of time so that application to a cold ware can be effected, i.e. without heating of the ware itself and all of its concomitant problems.